6.4 MgO dielectric response, Born charges and LO–TO splitting
These are unexecuted teaching inputs and starting models. Original diagrams are schematics, not calculated results. Validate version-specific syntax, licensed or authorized data, numerical convergence and the scientific model before using this workflow.
6.4.1 Model, units and provenance
PW cutoffs and energies use Ry, common force output uses Ry/bohr, and pressure uses kbar. Geometry cards state their coordinate units. Different executables have distinct grammars and time-unit conventions.
Shared inputs, conventions and evidence
6.4.2 Unexecuted inputs and explicit deltas
Use the accompanying instructions to identify the parent calculation and placement of every delta; a snippet is not automatically a standalone input. Preserve all blank-line and file-provenance requirements.
6.4.2.1 Input block 1
! MgO ground-state starting geometry: ibrav=2, A=4.21, nat=2, ntyp=2
! A is in Angstrom and must be relaxed/converged, not treated as a result.
ATOMIC_SPECIES
Mg 24.305 Mg.PBE.UPF
O 15.999 O.PBE.UPF
ATOMIC_POSITIONS crystal
Mg 0.0 0.0 0.0
O 0.5 0.5 0.5
6.4.2.2 Input block 2
MgO Gamma dielectric response
&INPUTPH
prefix='mgo', outdir='./scratch/mgo', tr2_ph=1.0d-14,
fildyn='mgo.G.dyn', epsil=.true., ldisp=.false.
/
0.0 0.0 0.0
6.4.2.3 Input block 3
6.4.3 Worked investigation
6.4.3.1 Intuition and prerequisites
In a polar insulator, a long-wavelength longitudinal vibration creates a macroscopic electric field. Electronic dielectric screening and Born effective charges determine the nonanalytic correction near Γ. Use a converged insulating rocksalt MgO primitive cell with compatible Mg/O pseudopotentials, fixed occupations and well-relaxed geometry. A metallic smearing setup is not an interchangeable starting point for this dielectric calculation.
6.4.3.2 Original structural and response delta
See input block 1 above.
6.4.3.3 Checks, pitfalls and exercise
Test charge neutrality through the sum of Born tensors over atoms, dielectric symmetry and convergence versus k mesh/cutoffs. Distinguish the clamped-ion electronic dielectric tensor ε∞ from the static dielectric response including ionic motion. For interpolated polar dispersions, carry the long-range electrostatic information correctly through q2r/matdyn; 2D materials require different long-range treatment, not a bulk formula with added vacuum. Exercise: explain the directional Γ limit and why a single undirected “Γ optical frequency” may be incomplete for a polar solid.